For many American museums, the Harlem Renaissance painter Aaron Douglas (1898-1979) is an almost Vermeer-like figure, whose shadowy, graphically powerful depictions of African-American themes appear so rarely on the market that when canvases surface, curators pounce. And that is exactly what the Metropolitan Museum of Art and the National Gallery of Art in Washington did recently. Each institution has acquired one of his major paintings, which were sold by a private collector who had purchased them from Douglas himself the year before his death.

The Met’s painting, “Let My People Go,” from 1935 to 1939, an angular lavender-and-gold depiction of Moses in Egypt from the Book of Exodus, has just gone on view in the museum’s Lila Acheson Wallace Wing for modern and contemporary art. The National Gallery’s work, “The Judgment Day,” a 1939 composition of a black, trumpet-blowing angel Gabriel that was bought last year and treated for several months by conservators, goes on view this summer in the museum’s American galleries. Both works are based on Douglas’s highly regarded series of illustrations for James Weldon Johnson’s 1927 poetry collection, “God’s Trombones: Seven Negro Sermons in Verse.” Neither institution would identify the collector or the price paid, though paintings by Douglas, who was born in Topeka, Kan., and spent 15 years working in New York, have generated high six-figure prices at auction.

Randall Griffey, an associate curator at the Met who was involved in the acquisition with the help of the Alexandre Gallery in Manhattan, said he and Sheena Wagstaff, who leads the museum’s modern and contemporary department, had long been trying to build on the Met’s strength in early-20th-century works on paper by African-American artists and were on the hunt for major paintings.

“We could never have imagined at that point that we’d have the opportunity to get something quite as spectacular as we did,” Mr. Griffey said of the painting by Douglas, whose influence can be seen directly or indirectly in the works of contemporary artists like Kerry James Marshall, who as a college student first saw Douglas’s “Let My People Go” in an exhibition in Los Angeles. “He casts a very long shadow through the 20th century.”

LABOR PROTESTS DRAW RESISTANCE

Activists who have been working to draw attention to labor practices in connection with the Guggenheim’s planned expansion in Abu Dhabi — and who last week briefly occupied the loading dock of the Peggy Guggenheim Collection in Venice during the 2015 Biennale — said this week that their tactics seemed to be generating more overt resistance from the government of the United Arab Emirates, which oversees cultural construction projects.

Walid Raad, an influential contemporary artist and member of Gulf Labor, one of the groups protesting labor conditions, said he was prevented from entering the country last week to conduct research, after having made several such trips previously. At the airport in Dubai on Monday, on his way to board a plane to Abu Dhabi, he said, he was taken into a waiting room and relieved of his passport by immigration officials.

“They came back about two hours later to tell me I was being denied entry for quote unquote ‘security concerns,’ ” said Mr. Raad, who was born in Lebanon and works in New York. On Tuesday, his passport was returned, and he was put on a flight back to New York. The incident comes after a previous denial to Andrew Ross, a New York University professor and Gulf Labor member, who was prevented from boarding a plane to Abu Dhabi in March to conduct research among workers. Ashok Sukumaran, an artist based in Mumbai and a member of the group, was also refused entry this month.

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“Let My People Go” was acquired by the Met.CreditAll Rights Reserved, Aaron Douglas/Licensed by VAGA, New York, NY, Metropolitan Museum of Art

“I’m an artist whose work is in the collection of the Guggenheim, and I’m a recipient of a Guggenheim fellowship,” Mr. Raad said, adding that he had asked Guggenheim officials to try to rectify the situation. “I’ll be naïve and say that maybe these bans are just a clerical error that will be fixed.”

Gulf Labor members contend that Abu Dhabi workers, many of them migrants, are exploited financially, given poor housing and subject to brutal work schedules. Guggenheim officials have said they are able to exert little influence over construction and labor practices in the city. They point out that construction of the museum in Abu Dhabi has not yet begun and that they are working with government officials in the United Arab Emirates to try to ensure fair labor policies.

On Wednesday, Tina Vaz, a Guggenheim spokeswoman, said the museum “understood the seriousness” of Mr. Raad’s situation and had made inquiries. But she added that immigration issues “are outside our sphere of influence.”

ROCKWELL SHOW AT UNITED NATIONS

As the United Nations prepares to celebrate the 70th anniversary of its founding this year, it is also at work on an unusual art exhibition that will retrieve from deep in the archives its brief connection with one of the most beloved American artists of the 20th century, Norman Rockwell.

A mosaic based on Rockwell’s 1961 painting “The Golden Rule” has been a popular draw at the United Nation’s headquarters since it was given as a gift to the institution in 1985. But a massive charcoal drawing that served as an inspiration for “The Golden Rule,” a 1953 work called “United Nations,” which Rockwell made after visiting the United Nations in 1952, has been little seen. With the exhibition “We the Peoples: Norman Rockwell’s United Nations,” on view at the United Nations Visitors Center from June 29 through Sept. 15, the work, which Rockwell never turned into a painting, will be exhibited for the first time outside its home at the Norman Rockwell Museum in Stockbridge, Mass.

“To me, it’s been a complete revelation,” said Jan Eliasson, the deputy secretary general of the United Nations. In a brief moment between dealing with crises in Syria and Ukraine, he traveled to Stockbridge last year to see the drawing — which teems with idealized faces of people from around the world and also depicts actual diplomats of the time, like Henry Cabot Lodge Jr., then the United States ambassador to the United Nations.

The exhibition will feature 33 original Rockwell artworks, including sketches and color studies, along with notes and source photographs taken for “The Golden Rule” and “United Nations.”

“I think for us to show this here in New York, to show Rockwell being the bridge between the international and the local, so to say, is very important,” Mr. Eliasson said. “It makes you realize how deep his sense of justice was, and how much he was a citizen of the world.”

A version of this article appears in print on , on Page C20 of the New York edition with the headline: The Met and the National Gallery Buy Harlem Renaissance Paintings. Order Reprints | Today’s Paper | Subscribe

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